Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
  • G01S3/80—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
  • G01S3/802—Systems for determining direction or deviation from predetermined direction
  • G01S3/808—Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
  • G01S3/8083—Systems for determining direction or deviation from predetermined direction using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems determining direction of source
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
  • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/18—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using ultrasonic, sonic, or infrasonic waves
  • G01S5/22—Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements

Definitions

• This disclosure relates generally to distributed fiber optic sensing (DFOS) systems, methods, and structures. More specifically, it pertains to the detection and localization of acoustic events across a city-scale environment using DFOS.
• DFOS distributed fiber optic sensing
• DFOS Distributed fiber optic sensing
• DFOS distributed fiber optic sensor
• systems, methods, and structures that monitor an entire community including a city or other urban environment(s) using acoustic DFOS techniques.
• our inventive method that analyzes acoustic events and localizes their source(s).
• systems, methods, and structures according to aspects of the present disclosure effectively transform fiber optic cables - that may already be deployed in an environment such as telecommunications cables - into a “microphone array” that advantageously permits detecting and locating acoustic events while discriminating acoustic events of interest from normal, everyday acoustic events that occur in such a setting.
• DAS distributed acoustic sensing
• FIG. 1 is a schematic diagram of an illustrative distributed fiber optic sensing system and operation generally known in the art;
• FIG. 2 is a flow chart illustrating the operation of DFOS according to aspects of the present disclosure;
• FIG. 3 is a schematic diagram showing an illustrative physical layout of an acoustic event detection according to aspects of the present disclosure
• FIG. 4 is a plot of a waterfall graph showing both time and spatial characteristics of an acoustic event according to aspects of the present disclosure
• FIG. 5 is series of plots showing time domain signals received at selected virtual microphones according to aspects of the present disclosure
• FIG. 6 is series of plots showing running variance of selected virtual microphones as a function of sample number according to aspects of the present disclosure
• FIG. 7 is series of plots showing running 1/p values of the virtual microphones according to aspects of the present disclosure.
• FIG. 8 is a plot showing a calculated most probable acoustic event (gunshot) location shown on a 2D map according to aspects of the present disclosure
• FIG. 9 is a plot showing a heat-map-like demonstration of possible acoustic event location (gunshot) shown on a 2D map according to aspects of the present disclosure
• FIG. 10 is a birds-eye view plan of our illustrative test bed according to aspects of the present disclosure.
• FIG. 11 is a plot showing an illustrative waterfall image of an acoustic event detected by DAS in which each ellipse corresponds to a different sensor point for our illustrative experimental testing according to aspects of the present disclosure
• FIG. 12 is a plot showing detected acoustic event by four reference points a) spool, b) pole, c) pole 2 and d) pole 3 for our experimental testing according to aspects of the present disclosure.
• FIG. 13 is a plot showing illustrative source locations together with actual source locations on test bed map for our experimental testing according to aspects of the present disclosure.
• FIG. 1 is a schematic diagram of an illustrative distributed fiber optic sensing system generally known in the art - we begin by noting that distributed fiber optic sensing (DFOS) is an important and widely used technology to detect environmental conditions (such as temperature, vibration, stretch level etc.) anywhere along an optical fiber cable that in turn is connected to an interrogator.
• DFOS distributed fiber optic sensing
• contemporary interrogators are systems that generate an input signal to the fiber and detects / analyzes the reflected/scattered and subsequently received signal(s). The signals are analyzed, and an output is generated which is indicative of the environmental conditions encountered along the length of the fiber.
• the signal(s) so received may result from reflections in the fiber, such as Raman backscattering, Rayleigh backscattering, and Brillion backscattering. It can also be a signal of forward direction that uses the speed difference of multiple modes. Without losing generality, the following description assumes reflected signal though the same approaches can be applied to forwarded signal as well.
• a contemporary DFOS system includes an interrogator that periodically generates optical pulses (or any coded signal) and injects them into an optical fiber.
• the injected optical pulse signal is conveyed along the optical fiber.
• a small portion of signal is reflected and conveyed back to the interrogator.
• the reflected signal carries information the interrogator uses to detect, such as a power level change that indicates - for example - a mechanical vibration.
• the reflected signal is converted to electrical domain and processed inside the interrogator. Based on the pulse injection time and the time signal is detected, the interrogator determines at which location along the fiber the signal is coming from, thus able to sense the activity of each location along the fiber.
• FIG. 2 is a flow chart illustrating the overall operation of DFOS according to aspects of the present disclosure.
• operation of our inventive system and method begins with an acoustic event happening within a surveillance area - i.e., that geographical area in which a sensing fiber is operational.
• a surveillance area i.e., that geographical area in which a sensing fiber is operational.
• such sensing fiber may be deployed as part of our sensing system - or may be previously deployed and operating to convey telecommunications or other data traffic.
• Such an acoustic event produces an acoustic vibration in the air which is then detected by the fiber optic cable.
• Such vibrations may advantageously be detected by a DAS system - including interrogator and analysis system and / or Al - based system - which is / are located in a central office - or other location including cloud systems - away from the actual acoustic event.
• a DAS system - including interrogator and analysis system and / or Al - based system - which is / are located in a central office - or other location including cloud systems - away from the actual acoustic event.
• - detected signals resulting from the acoustic event(s) are analyzed using our inventive method(s) including both spatial domain, and temporal domain analysis.
• a spatial domain analysis - determines which point(s) along a sensing fiber optic have detected an acoustic disturbance / signal, and those points are selected as our virtual microphones.
• our inventive method determines a time of arrival of the signal(s) for each virtual microphone. Once a time signature is determined for each virtual microphone, the location(s) (i.e. the coordinates) of this acoustic event is determined as a probability distribution on an actual map, based on the physical location(s) of the virtual microphones.
• FIG. 3 is a schematic diagram showing an illustrative physical layout of an acoustic event detection according to aspects of the present disclosure. As may be observed from that figure, several utility poles are shown suspending a length of fiber optic (sensing) cable that is further optically connected to a distributed acoustic sensing (DAS) system that may be conveniently located in a central office or other convenient location.
• DAS distributed acoustic sensing
• FIG. 4 is a plot of a waterfall graph showing both time and spatial characteristics of an acoustic event according to aspects of the present disclosure. From this plot, those skilled in the art will know that the time and position of the strain(s) induced by vibration patterns may be determined.
• a set of “virtual microphones” are selected.
• the virtual microphones” selected are generally those locations along the fiber optic cable route exhibiting the most sensitivity to strain and hence, acoustic events. Such understood locations include - for example - a down-lead fiber optic cable along a pole, a spool of fiber optic cable, fiber optic connection points to a pole, or a central part (substantially midpoint) of a fiber optic cable length.
• signal(s) recorded by each of these microphones is/are analyzed using a change point detection algorithm such as a Z- test, and the time of arrival is calculated for each microphone.
• FIG. 5 is series of plots showing time domain signals received at selected virtual microphones according to aspects of the present disclosure. As is shown in those plots, each of the individual virtual microphones (Virtual M-l, Virtual M-2, Virtual M-3, and Virtual M-4) each indicate different detected strain (acoustic) characteristics experienced at each of the individual virtual microphone locations along the sensor fiber optic cable.
• FIG. 6 is series of plots showing running variance of selected virtual microphones as a function of sample number according to aspects of the present disclosure. As may be observed and as shown in this series of plots in the figure, the differences in running variance for each of the virtual microphones of FIG. 5.
• FIG. 7 is series of plots showing running 1/p values of the virtual microphones of FIG. 5 and FIG. 6 according to aspects of the present disclosure. As may be observed from this figure, a “change point” may be selected for each virtual microphone.
• this determination may be output in at least two convenient and informative formats.
• a single location for the acoustic event source can be displayed on a 2-dimensional map.
• Second, and perhaps more informative, system noise and imperfections may be considered to further improve the results and a heat-map- like distribution map can be generated for the source location. When so displayed, a greater probability location may be readily determined from the map.
• FIG. 8 is a plot showing a calculated most probable acoustic event (gunshot) location shown on a 2D map according to aspects of the present disclosure
• FIG. 9 is a plot showing a heat-map-like demonstration of possible acoustic event location (gunshot) shown on a 2D map according to aspects of the present disclosure.
• the DAS system was operated at an optical pulse width of 40ns, at a pulse repetition rate of 20 kHz.
• the spatial resolution of the system was -1.22 meters.
• the locations of the poles and the fiber spool along the fiber optic cable were obtained by analyzing the DAS data of manual hammer hits at each location.
• a .32 caliber starter gun shooting short black powder blanks was utilized as the impulsive acoustic source, and fired once at 4 different locations, above head level approximately 2 meters above the ground at the testbed.
• the DAS signatures of each shot are recorded separately and analyzed to calculate the location of the impulsive acoustic event.
• FIG. 11 is a plot showing an illustrative waterfall image of an acoustic event detected by DAS in which each ellipse corresponds to a different sensor point for our illustrative experimental testing according to aspects of the present disclosure;
• the starter gunshot events are illustrated in a “waterfall” trace plot in the figure, which is a 2D representation of the detected DAS signal along the interrogated fiber length (x-axis), and how it changes in time (y-axis) where the signal strength may be color- coded. This figure shows a total time duration of 150 milliseconds at the fiber range between 300m - 550m.
• the same acoustic event is detected by different parts of the same aerial fiber optic cable (aerial is another term for cables suspended from utility poles) at slightly different times shown with red ellipses.
• TDOA time difference of arrival
• FIG. 12 is a plot showing detected acoustic event by four reference points a) spool, b) pole, c) pole 2 and d) pole 3 for our experimental testing according to aspects of the present disclosure.
• the threshold (p-value) in our algorithm was chosen as 0.001, so the earliest data value with a probability below this threshold is registered as a change point, and its time coordinate is taken as the signal arrival time.
• x. y, and z are the standard coordinates.
• the subscripts s, i, and j are denoting the “source”, i-th sensor, and j -th sensor respectively and c is the speed of sound taken as 343 m/s, and An/ is the relative time difference of arrival between i-th and j -th sensors.
• FIG. 13 is a plot showing illustrative source locations together with actual source locations on test bed map for our experimental testing according to aspects of the present disclosure.
• Telecommunication fiber optic cables including those deployed and operating to actively carry telecommunications traffic.
• Our experimental results verify our approach of integrating DAS technology to existing aerial telecommunications fiber optic networks for smart city and safer city applications that advantageously reduce installation costs associated with such systems.
• systems, methods, and structures according to aspects of the present disclosure may advantageously provide for the use of DAS for continuous monitoring of a large area for acoustic impulse events by employing fiber optic cables already deployed in an urban setting as a “microphone array”.
• our inventive techniques employ DAS for detection and localization of acoustic impulse events by using time-frequency-spatial domain methods for data analysis including using spatial distribution of the fiber optic as part of sensing configuration and using frequency filtering optimization to preprocess the data, using timedomain change point-detection method for relative time of arrival estimation and formulation of the localization as an optimization problem (rather than equation solving) to estimate the event location (using multiple measurements), with a notion of uncertainty quantification and then informing relevant authorities on the detected event time and location(s).

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• 2021
  • 2021-08-24 US US17/409,792 patent/US20220065977A1/en not_active Abandoned
  • 2021-08-25 WO PCT/US2021/047621 patent/WO2022046949A1/en active Application Filing
  • 2021-08-25 DE DE112021004482.6T patent/DE112021004482T5/de active Pending
  • 2021-08-25 JP JP2022578820A patent/JP2023538196A/ja not_active Withdrawn

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